(1) Field of the Invention
The present invention relates to an image forming apparatus such as a digital copier, printer unit for a facsimile machine, digital printer, plotter etc., and more particularly relates to an image forming apparatus in which an image is formed on a recording medium by causing the developer to jump thereto.
(2) Description of the Prior Art
There have been known image forming apparatuses which, in accordance with an image signal, form a visual image on a recording medium such as paper etc.
Japanese Patent Application Laid-Open Hei 7 No. 47,708, for example, discloses an image forming apparatus wherein charged particles are placed in an electric field so that they will jump by electric force to adhere to the recording medium whilst the potential to be applied to the control electrode having a number of passage holes located in the jumping passage is being varied, to thereby form a latent image on the recording medium, and during this, dust-sized particles are removed from the charged particles to be transferred for development.
More specifically, in this prior art technique, the charged particles held on a grading roller are caused to jump to the toner support roller by the reactive force arising during elastic collision of the charged particles against the blade, so that only the charged particles from which the dust-sized component has been removed will be transferred to the toner support roller. The thus selected toner on the toner support roller is controlled and made to jump by the control electrode.
The above prior art technique, however, did not take into account the bulk density of the developer. Therefore, this method includes the problem that the printed result fluctuates due to the variations in bulk density of the developer.
As a result, the current situation is that open selection of the developer is not possible from a point of view of cost performance and/or user's taste when the developer is used for an image forming apparatus such as a digital copier, facsimile machine, digital printer, plotter etc.
It is a critical and important problem that the processing of an image be controlled appropriately with regard not only to the distribution of size of the developer particles but also to bulk density of the developer, in order to form satisfactory images regardless of variations in bulk density of the developer.